The present invention relates generally to an adapter assembly for joining two rotatable members and a related power transmission assembly. In particular, the present invention relates to an adapter assembly for closely joining an output shaft of a motor with an input shaft of a speed reducer.
Speed reducers of various types are known for converting output speeds and torques of prime movers such as motors to desired speeds and torques for an intended application, such as driving conveyors, rotating machinery, and the like. Generally, such speed reducers include one or more intermeshing gear sets arranged on a series of shafts between an input and an output. The input is designed to be connected to the prime mover, while the output, typically a keyed shaft or sleeve, is connected to the machine application to be driven. Multiple gear sets may be employed for further reduction of speed beyond the limits of a single gear set. For example, two-stage and three-stage speed reducers are commonly employed. A three-stage reducer may be created by combining a base reduction gear set within one housing with a modular additional reduction gear set within an additional housing secured to the main housing. Typically, two reduction gear sets are provided in the base reducer and a third reduction gear set is provided in the additional reducer, although all three gear sets can be included in the base reducer.
Motors of various constructions are also known for providing output rotation. Typically, output is provided by a shaft extending from a substantially flat end of a motor. One conventional form of electric motor interface includes a so-called "C-face" electric motor frame having a machine interface surrounding the electric motor output shaft. Other electric motor interfaces include the IEC B5 or IEC B14 flanges. The machine interface is designed to be coupled directly to a supporting flange, such as extending from a gear reducer or other device, or from an adapter joined to the reducer or device.
Various constructions are known for joining the output of the motor shaft with the input to the reducer shaft. Because of the various different types of motors having different frame sizes and power ratings and the different types and configurations of speed reducers used, numerous configurations of adapter assemblies for joining the motors and reducers are required. Thus, a problem in structuring speed reducers of the type mentioned above resides in interfacing the speed reducer input shaft with the electric motor. It is generally known in the art of speed reducer mechanical interfaces to provide an adapting shroud or flange which is bolted directly to the electric motor C-face and surrounds a coupling interfacing the electric motor output shaft to the reducer input shaft. This form of interface has the advantage of facilitating mounting of the motor and reducer set for providing acceptable alignment between the motor and gear reducer shafts.
In one type of interface typically referred to as a "gear motor," an input pinion of the reducer is mounted directly to the motor shaft, such as by press-fitting or keying the pinion around the motor shaft. A short interface casting is attached to the reducer housing and the motor frame. The motor shaft-mounted pinion extends into the reducer and meshes with a corresponding gear to form the initial reduction gear set.
In another type of interface, an intermediate drive shaft assembly, or "jack shaft" assembly is provided between the reducer and the motor. This assembly includes a pair of bearings supported in the jack shaft assembly housing to support the jack shaft. The motor has two of its own bearings to support its own shaft within the motor housing. The jack shaft either may be coupled to the electric motor shaft on its input side or may receive the electric motor input shaft into a bore formed in an end of the jack shaft. The output side of the jack shaft supports a pinion for the first gear set.
While both types of interfaces provide adequate transmission capabilities for reducers, they are not without drawbacks. For example, the jack shaft transmission assembly solution can result in a large number of separate adapter housing castings and jack shafts needed to accommodate various shaft lengths, and motor frame and reducer housing sizes. In particular, because a single-piece adapter housing is commonly used for both supporting and spacing the motor and the reducer, and for supporting the jack shaft between the motor shaft and the input gear set to the reducer, the design must accommodate various gear set center distances, electric motor frame sizes, reducer frame sizes, and motor and reducer shaft sizes. Thus, a large number of separately cast adapter housings and jack shafts are typically required to provide the desired range of gear ratios and power ratings. Depending upon the number of motors within a family of motors and the number of reducers with a family of corresponding reducers, literally dozens of separate adapter housings and jack shafts may be required to join motors to all suitable reducers.
U.S. patent application Ser. No. 08/792,201, filed Jan. 31, 1997 and owned by Applicant's Assignee, describes a system for reducing the number of different cast adapter assemblies required to join various motors and reducers through use of common sizing. The system is capable of accommodating a large variety of electric motor frame sizes and offers modularity through use of a jack shaft to interface with the first gear set of the gear reducer. The system permits reduction of the overall number of cast adapter housings, while offering the flexibility of the jack shaft input system.
The system operates well to significantly reduce the cost of manufacturing and inventorying the adapters. However, using adapters according to the system requires certain of the parts within the adapters to be sized to be able to handle the largest possible motor that may be used with the adapter. For example, the bearing located closest to the motor must be sized large enough to handle the largest (i.e., highest power rating) motor suitable for use with the largest speed reducer matable with the particular motor adapter. In some cases, the bearing is much larger and therefore more expensive than needed for the particular motor actually used. Similarly, jack shaft parts also may be sized larger than needed for particular applications to take into account the range of possible sizes of other components. Thus, the reduction in the number of adapters required provided by the common adapter system reduces material and inventory costs related to the adapters, but increases costs for other parts within the drive train which have to be sized larger than needed for some applications.
Regardless of whether the above adapter system is used, the drive train between the output shaft of a motor and the output of a two or three stage reducer may extend from several inches to several feet, depending on the size of the motor and the number of gear reductions used. Consequently, it is desirable in some applications to reduce the length of the power train along the axial direction of the output shaft.